text:
Why can't planes use only flaps in the tail section instead of stabilizers?
I imagine plane having only four flaps in the back (one on top, bottom, left and right), similar to ailerons but longer and narrower. They can open from the fuselage to correct the plane's yaw or angle. I predict that this would increase efficiency of the plane since there's no drag from the horizontal and vertical stabilizers.
Can this design work?

Re "They can open from the fuselage" -- are you imagine a surface hinged on the front edge, that lies flush against the fuselage when not in use? Like the speed brakes on a F-86 or F-15? If so, I think the answers posted so far have missed this point. Or do you mean surfaces just like the all-moving horizontal stabilizer on many current jet fighters, but that retract whenever not actively being deflected? The question needs more clarity. –

Your question is partly covered here regarding why the vertical stabilizer is important. The empennage (tail surfaces) of conventional planes provides both passive and active stability. Like the feathers on an arrow (which is where the word empennage comes from), they help the airplane to remain pointed in the direction of flight as well as providing active control surfaces. The cost of providing stability is added weight and drag, but if the surfaces are removed, the stability aspect will need to be provided manually, or alternately. This is how unconventional aircraft like the B-2 flying wing, or even modern fighter aircraft, are able to fly.
So, yes, we can fly airplanes without conventional tail surfaces. Some designers like Burt Rutan have created unconventional designs for general aviation. However, design changes will also have drawbacks. At the very least these designs behave differently than conventional planes, which requires special attention. The strange appearance is also reason for some pilots to distrust them.
If the plane is going to be unstable without computer control, that introduces safety problems. In military aircraft the pilots can eject when issues arise. But unlike modern commercial planes, the pilots cannot simply take over control if the computers fail.
There is also an aerodynamic issue with what you propose. Conventional control surfaces deflect the entire surface, so air continues to flow past both sides. However, if you only deflect one side of the surface, air is only flowing past the outer face. This acts like a spoiler and creates extra drag. Though this drag will be the force controlling the plane, it is not as efficient as moving a control surface. As Peter Kämpf pointed out, it is much more feasible to increase the effectiveness of the existing surfaces than to eliminate them.
Modern airliners represent a compromise between efficiency and safety based on currently available technology. Although alternate designs have been proposed, these configurations create their own unique problems.

Great answer! Though I don't understand why a moving surface is more efficient. Doesn't the rudder create just as much air resistance as the opening flaps I proposed?

@EwenW. you need some surface there to provide stability, and replacing that with a computer presents safety issues. I have edited my question to hopefully explain better.

Just a side question if you don't mind answering.. Approximately what percent of fuel consumption could the plane cut down assuming that it has no stabilizers and flies perfectly balanced (though highly unlikely).

@EwenW. I couldn't find a quick answer right now, maybe the drag of different airplane sections is worth a separate question.

@EwenW. Approximately 100%. Because it will crash and never fly again, therefore using no additional fuel. :)

First let me clarify: You propose four moving surfaces which extend as needed (I guess that is what you mean by "open from the fuselage") from the fuselage?
Yes, theoretically it can work, but the flaps need to be as big as the surfaces they are intended to replace and need to be out in the airstream  all the time. That would look remarkably like what we currently have, so any hopes of significantly reducing drag are unfounded.
Now there is a scenario where drag savings on the flaps are possible. Tail surfaces don't work at their maximum or even optimum lift (optimum meaning at their best lift to drag ratio) most of the time, so the degree of extension could be smaller, and less surface area is exposed. But where do you stow all the remaining part of the flap? Now you need to make the fuselage that much bigger, so you lose in fuselage drag what you gain in tail area drag. Add to this the weight of the kinematics for moving the flaps, and the conventional design looks ever more attractive.
As @fooot has pointed out, this scenario needs computer control and added layers of safety like secondary means of flap movement if the primary actuators fail.
If no asymmetric thrust scenario is possible, earlier designs have already proposed to do away with the whole vertical tail and replace it with a small, computer-controlled fin at the nose, yielding significant weight and drag savings.
Aircraft designers have constantly tried to reduce tail surfaces to the minimum they can get away with. Please look at the picture of the An-70 below closely: The horizontal tail has slats which open forward and up, so the tail surface can produce more downforce when flaps are extended. This is a trick to reduce the tail area, which doesn't need to produce much downforce during most of the flight, at the expense of more drag with flaps extended and more moving parts.

An-70 at Paris Airshow in 2000 (own work)

Thanks for the answer, but why do the flaps have to be out in the airstream all the time? Surely the plane can fly quite some distance without the need for adjusting the yaw or elevation, or am I missing something?

@EwenW.: If you want natural stability (no electronics, no redundancy, works all by itself), you need something at the back to produce an opposing force as soon as the aircraft deviates from the desired state. This works automatically, but only if the stabilizing surface is out all the time. With computer controlled stability, you still need something smaller out there to be able to react immediately. Since the aircraft is unstable without those tail surfaces, the smaller flaps need to move all the time, and need to do this much faster than the period of the fastest eigenfrequency of motion.

"at the expense of more drag with flaps extended"  Most of the times when you have flaps extended (landing, rejected takeoff), more drag is a good thing.

@ymb1 You guessed right.

Yes that is possible, but impractical.

Such a design would use asymmetrical drag to compensate for moments about the centre of gravity. Conventional tailplanes use asymmetrical lift, which has a much lower drag-to-force ratio.
The horizontal tailplane provides an additional spot for lift, so that there is a practical range of CoG locations. The bottom or top flap of the replacement design would have to be permanently deflected, again with higher drag.

It is possible to design such a system as a passive system though, like the designers of Kamov seem to have done.


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How minimum runway length is calculated for PAC P-750 XSTOL?
I'm not a pilot, but have interest in the question from a safety perspective, as a skydiver and drop zone operator.
I read the POH of PAC P-750 XSTOL, and tried reading a bit about the calculations, but could not make it out.
Given the parameters below, how is the minimum runway length is calculated for PAC P-750 XSTOL?
Parameters:

Pac 750 XSTOL
15 knots cross wind 90
0° flaps
6500 LBS TOW
Runway is 1500 feet above MSL
ISA +10°

I don't think you can.  The manual only lists takeoff performance data for 20° flaps and doesn't specify a correction factor for 0° flaps.  FWIW, even if the 0° data was there, you wouldn't need all of the parameters you specify.  A direct crosswind doesn't matter, since the headwind/tailwind component is zero.  ISA correction is calculated based on pressure altitude and air temperature and you only specify true altitude and no temperature, but since you already gave us an ISA correction we don't need them anyway.

You can't, at least not on the basis of the POH you linked. Taking off with 0° flaps for that aircraft is outside the POH limitations chapter.
2.20 Flap Limitations:

Approved flap ranges.
TAKEOFF FLAP: 20°
LANDING FLAP: 40°

4.27 Amplified Procedures - Normal Takeoff):

A wing flap setting of 20°  is recommended for all takeoffs. 20° flap
will provide the best takeoff performance. The Normal Takeoff
technique is to be used for Short Field operations and is the
technique used to derive the performance data in Section 5.

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Do aircraft technicians need additional certifications to work in other countries?
Professional technicians, who work in aircraft maintenance, usually obtain some sort of national certification, right?
Let's suppose someone got training and certification in one country, and wants to migrate to another country. Does he require some certification to work there as an aircraft technician? How is it achieved?

There are two parts to this question; one is the technical certification of the technician which has to match the regulations of the other country, the other part is about labour and migration laws. The latter part is out of scope here, the first part can only be answered if we know which countries you have in mind.

By 'migrate' I meant the migration of their technical certification to the target country, not the actual process of relocating. Really I just want to know if someone has gone through this or knows of someone who did, in any country combination.

In addition to what @DeltaLima said, do you think it would be easy is speculation, please think about removing or reformulating the question

I don't have personal experience, but this is absolutely something you can do.
Unfortunately many countries do not have the exact same standards or licensing scheme, so often your licence is not automatically converted, but you rarely need to start from scratch.
For example, if you wanted to come to Australia, you would need to attend a CASA approved Part 147 training organisation, which are located around the world. They will assess you, possibly provide you with some extra training, following which you can apply for an Australian Part 66 engineer licence. Once you get that licence you shouldn't have too much difficulty migrating, but that's a discussion outside of my league. More details on this conversion process are on the CASA website.

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Can Air Traffic Controllers participate in Q&A?
While asking the question in chat How do we get controllers on the site? @egid suggested there may be FAA or union restrictions on participating in Q&A. That would be sad since pilots and controllers communicating with each other improves safety and efficiency... but certainly doesn't mean it isn't true.
Does anyone know of specific restrictions placed on controllers by the FAA or NATCA (National Air Traffic Controllers Association) which would prevent them from answering questions on this site?
I realize this blurs the line slightly between the main site and meta, but I'm asking about legal reasons, not speculation about why we haven't attracted any controllers yet (that I'm aware of).

I am not aware of any legal limitation for air trafic controllers to speak out on a public website, but there could be one.
StuckMic.com is however an ATC forum in which FAA ATCo's seem to participate actively. This leads me to believe that they are allowed to speak out on a public website. There are very likely restrictions on what they can share.

StuckMic.com requires a logged in account to view threads, so not completely public.

The full FAA regulations covering controllers can be found at http://www.faa.gov/documentLibrary/media/Order/ATC.pdf.
Looking through the table of contents (page 25 onwards), I couldn't find anything related.
I also searched the document for the phrases: forum, internet, online, discuss - nothing relevant was found.
Furthermore, the ATCA (Air Traffic Control Association) has been running annual conferences on air traffic control for 58 years, where they obviously discuss ATC; and they also have members of the FAA on the committee.
I've searched Google too, and can't find anything relevant.

The 7110.65 covers ATC procedures. Social media posting, etc, is covered under various other policies and laws, such as the FAA's Human Resource Policy Manual, the NATCA/FAA Collective Bargaining Agreement, the Hatch Act, etc. You would not expect to find anything regarding social media in the 7110.65 in the first place.

In conventional forums (i.e. in person), the FAA even organizes interactions with controllers. Here is an example of a Pilot-Controller forum for Livermore Airport, in Northern California, organised by the FAASTeam team.
https://www.faasafety.gov/SPANS/event_details.aspx?eid=47646
A search for the term "controller" indicates that such interactions are common: https://www.faasafety.gov/SPANS/events/EventList.aspx
I have seen similar presentations involving controllers which are web-based, and which are followed by Q&A sessions with participants.

Yeah, I've been to those sorts of sessions before. I don't think they directly translate to interacting on web forums, but ultimately I think the answer is probably that they can participate, but that not many are participating here.

I've seen controllers on web forums, but never in an official capacity. They've always identified with something like "I am a controller, and from my work experience XYZ..."

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text:
Is there a minimal approach speed for airliners during rush hour?
For busy airport, sequencing can be complexe. If the ATC put all aircraft in front of each other with the correct separation (which can be really small for busy airports) in final, if the airliners' approach speed vary significantly, one plane could catch up the preceding one. Can the ATC ask for a pilot to increase its approach speed up to a minimum speed?

Separation is not ever "really small" (unless the controller has made a serious error).  I don't think it's really common for airliners (since they have pretty well known approach speeds), but if you're flying a GA plane & mixing with commercial traffic, it's pretty normal for the tower to request you to maintain a higher than normal approach speed.

@jamesqf  "really small" may be too subjective. It is not uncommon to have landings separated by less than 2 minutes. Too me this is kind of no much (even if this is enough)

"Rush hour" xD...

@Cloud: google for "plane movements worldwide animation" and check out the flood of aircraft arriving from North America eg. at London in the morning. Like this one: https://www.theguardian.com/world/video/2014/jul/03/transatlantic-flight-paths-of-2-524-planes-on-single-day-video-animation. That's the rush hour for arirports :-)

@Cloud take a look at the NATS (the ATC for the U.K.) blog to see the ebb and flow of air traffic - https://nats.aero/blog/2014/11/take-guided-tour-uk-skies/

@Manu H: Two minute separation is plenty, except maybe in the case of a light plane following a heavy, where you might have problems with the wake turbulence not disapating.

ATC can not only ask for a minimum speed, but rather instruct each aircraft to (more or less) exactly fly at a particular speed. This is essential for maintaining separation. As J. Hougaard pointed out in the comments, the speed on the last 4 NM is always up to the pilot to slow down to final approach speed.
It is the duty of the pilot to evaluate if it is safe to comply with this restriction. In case the aircraft cannot fly as slow as asked for, the pilot can simply reply UNABLE and ATC will either try to make it work or instruct the aircraft to go around.
Some airports also publish speed restrictions on the approach charts. This is an example of a minimum speed from the ILS approach into 01L/R at Stockholm-Arlanda (ESSA):

More precise speed restrictions are for example given on the STAR charts of the (now closed) Istanbul-Atatürk airport (LTBA):

To augment this (good answer), ATC has specific guidelines for what speeds they can assign. In the U.S., FAA order 7110.65 section 5-7-3 spells it all out - for aircraft on approach, basically 170 knots or greater for jets and 150 knots or greater for turboprops and pistons (if able). Other civil aviation authorities may have similar guidelines. (It appears ICAO does not.)

Might be worth adding that ATC generally speaking has no control over aircraft speed within 4NM final. At that point, speed is entirely up to the pilots, since they need to establish a stable approach.

@J.Hougaard Thanks, added.

From my experience in busy airspace (Chicago, New York, San Francisco), ATC will ask you to maintain a specific speed until the final approach fix. Usually this speed is faster than what you'd ideally be doing at that position. After the FAF, you can slow to the appropriate final approach speed. It's true that approach speeds vary depending on weight and weather conditions - ATC knows this and expects it, but the spacing is adequate for aircraft with variable approach speeds the last 4 miles of the landing.

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text:
What is the significance of the exclamation mark (!) on ACARS page of a Boeing 737?
For a while now I've noticed an exclamation mark on the ACARS inflight page of the B737NG at the beginning of a flight. It is located in the top left corner of the page and it just disappears after a while. I've been searching high and low what it means but can't find it.
Any ideas?

I presume this is on a flight sim?

No, it's on a real plane

Not sure what options Boeing offers on the 737NG, but I assume this is a Honeywell product?

Yes, it's a Honeywell. FMC is 10.8 but I don't know if there is a specific acars/datalink version.

The ACARS menus can be customized by the airline/operator. They have a PC based configuration tool that can be used to add and modify menu items and messages. Perhaps this is specific to your company.

Ah, Thanks. I'll put out the request there!

If it is company specific, and if you're allowed, please be sure to come back to tell us what it means. Feel free to answer your own question.

If it's company specific make sure they don't mind you posting it first.

@GdD, that was the and if you're allowed part... ;)

Okay guys, the verdict is in.
It is a symbol to indicate the crew alerting chimes are inhibited.
From OUT (off block) until OFF+15 and estimated ON-10 until IN (on block) the chimes to alert for new data and messages are suppressed to avoid nuisance warnings during critical flight phases.
Happy landings!

On other FMC configurations, the chime is only inhibited below some flight level, e.g. FL230.


text:
Is it possible to drop a payload via anchored parachute?
Apologies if this is not the proper forum for this question -
Here's my situation:

I'm trying to drop a payload via parachute with some accuracy.  I'm worried that in the above setup, the line will interfere with parachute deployment or - if not deployment - operation during flight (imagine wind pushing the chute into the line).
I haven't tested this yet but plan to.  Does anyone know how the payload <> anchor connection might be engineered to ensure full deployment throughout the descent?

Instead of a parachute, could you have a slowed descent by gripping the line a little tighter?

@SnakeDoc - we've considered a slow-release pulley but unfortunately our "brand" depends on the parachute as a means of deployment.

In that case, I believe it was Mythbusters (no idea what episode(s)) who used a 4 line (in a square) from the air-to-ground and the object was attached to all 4 lines. So when it fell, the 4 lines kept is centered. Maybe a similar idea would work for you (more anchor lines).

@SnakeDoc I hadn't thought of that.  But yet another constraint is a single line.  Really our only variable here is the connection between the anchor line and the payload... I know that doesn't give us much to play with.

Hmm, I'm afraid I have no other ideas. I think, depending on your environment conditions, you do run the risk of the parachute getting snared and preventing a good deployment. If your question doesn't get more attention here, I'd try over on the Engineering exchange - http://engineering.stackexchange.com/

Thanks @SnakeDoc.  I've actually posted there and got the suggestion to run the anchor line directly through the center of the parachute... I might try that.

I'm afraid this has nothing to do with aviation, so off-topic.

unfortunately our "brand" depends on the parachute as a means of deployment – nothing like letting your brand dictate engineering solutions! This seem backwards to anybody else?

I'm trying to drop a payload via parachute with some accuracy.
Cut a hole in the middle of the parachute, make its edge smooth and install a pipe through the center of the box that contains the payload. Run the line through the pipe and parachute and let the payload fall from the balloon. I believe the trick will work for small parachutes able to deliver up to 10 kg to the ground.

If the hot air balloon is well anchored you can probably just use your original plan.  The winds aloft will push the balloon in the direction the wind is going, so the anchor rope should be at an angle relative to the ground.  When you drop the parachute, those same winds should keep the parachute/payload pushed clear of the anchor rope.  So long as the drag rope connecting the payload to the anchor rope is sufficiently long and the mechanism connecting the drag rope to the anchor rope is sufficiently slippery, you shouldn't have a problem.
I worry about Energizer777's solution though.  Mainly because the rope might be angled because of the winds aloft, as stated before.  Payloads on a parachute like to hang right below the parachute (more or less), and if the angle on the rope is sufficient the payload will simply end up resting on the rope itself, which might foul up and collapse the parachute since it's load will not be pulling on it properly.
All of that being said, that solution will work if you do this on a day with very calm, or non-existent wind...

The problem is that you can't fix the angle with a single beam. Instead, use the following setup (90 degrees rotated for ASCII art):
            ,<)           __
/___________A____________/  \
\                        \__/

That is to say, use two beams to guide two rings along the anchor rope, and connect the parachute to the top of the A. Furthermore, connect the payload to the middle of the A (below the connecting bar) to balance the air friction of the parachute and the rope friction on the other side. This reduces the tilting torque.


text:
Can you help me to identify a Boeing 727 maintenance task involving a safety risk for a research project?
I need help identifying a Boeing 727 maintenance task that would be suitable for a research project on improving maintenance instructions.
Ideally, the task should meet the following criteria:
- the task should take about 1 hour to complete in a base maintenance environment;
- the task should have a safety risk that is prone to human error (for example, potential to do an incorrect installation of a component).
This is for a research proposal to improve the quality of maintenance instructions. I have a commercial aviation training school that is interested in participating. They have a 727 which is a type I've never worked on and I don't have access to any of the 727 manuals either.
I'm trying to table several options that I can put to the school. What I have so far is removal/installation of an AC generator or perhaps the generator constant speed drive. Further suggestions would be very much appreciated!

It's been a while since I worked the 727. It was a very forgiving airplane, so you had to do a lot to make a critical safety error from a maintenance perspective.
However, I do remember elevator position transmitters being a major pain to adjust. Although the manual wasn't necessarily bad, I never felt comfortable with the adjustments because of how sensitive they were. The manual made it sound so easy, when in all reality, I would have felt better if there was some note that said something to the effect of "this may take a while." Plus, you always had Skydrol dripping in your face when doing it off a lift in the howling wind.
Even tightening the bolt of the transmitter down was enough to bring it out of tolerance. So, ordinarily, you had to rig it out of tolerance, then hope that the tightening of the bolt brought it in tolerance. Sometimes it'd take 5 minutes. Other times it could take all night.
There is also a "dog bone" that attaches between the transmitter and the flight control surface. Sometimes the bearings in that dog bone would develop slop, and cause autopilot issues as well.

I read Skydrol as Skydrool and thought you meant rain. I'm guessing that's some kind of lubricant or hydraulic fluid, instead.

Yes. Skydrol is a mechanic's favorite. It's an Esther based hydraulic fluid that burns like crazy when it touches your skin. It's usually found in places where you have to look straight up so that it can drip in your eyes. It's corrosive as hell too.

Thanks @Frank. Is a removal / installation of the transmitters a one man job? As for Skydrol... You used to be able to tell apart the mechanical from the avionics guys in the hangar: early onset of grey hair thanks to close encounters with Skydrol!

As I recall, the transmitter replacement itself is a one man job. The adjustment of it is usually a two man job. I'm pretty sure you need someone in the cockpit with a breakout box and a multimeter checking for null voltage. However, I believe you could fashion a breakout box for the connector at the transmitter and read it at the tail. In that case, you would only need one person.


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Is the A350 more efficent than the B787?
I have wondered this because the Trent 1000 engines are very similar to the Trent XWB engines on the 787. And if the A350 has better efficiency then why do so many airlines purchase the 787?

I feel these should be split in different questions.

Honestly, these kinds of comparisons are hard to do without proprietary information because a lot of the numbers aren't public and efficiency can be measured many different ways. The most common is probably fuel per passenger-mile, but that depends on each individual airline's seating configuration and also ignores any other revenue cargo that might also be on board. And all fuel efficiency numbers will vary with weight, temperature, altitude, exact course, distance flown, etc., which vary from one flight to the next, let alone one aircraft to another.

Don't forget other market considerations like the fact that 787 was to the market earlier.

The answer as to why companies seem to be favoring the 787 over the A350 is in several parts, none having very much to do with efficiency.
First, a grand total of just 6 A350 XWBs have been built. The A350 is just ramping up production this year, while the 787 has been in production about 5 years now. The 787's teething problems have spurred some interest in its competitor, but as the first composite airliner to start accepting orders, the Dreamliner has a distinct first-mover advantage.
Second, Airbus has seen some production problems in its larger airliners, which tends to make airlines nervous. The A380 saw cancellations totaling over $10 billion in lost revenue primarily due to its inability to make them fast enough, causing Airbus to indefinitely delay production of freight variants that major shipping companies were waiting for. Smaller, older production lines have been doing better but the A380 line is still taking up a lot of Airbus's resources that could be spent making 350s.
Third is simple cost. A 787-8's base price is about \$225 million. An A350 starts at about \$270 million. \$45 million a plane is nothing to sneeze at; it means you can have 6 Dreamliners for the cost of 5 A350s, and the major airlines are buying 40-50 of these planes each so the savings is considerable.

You should also mention the seat number that are not the same (although it is really close: 242 to 335 for the 787, 280 to 366 for the A350)

@ManuH that is true, however the seating numbers are so close with so much overlap that the actual price of each aircraft per passenger seat (and thus the required number of flights to break even) will be dependent on the exact specs of the airline's order.


text:
Is there any way to tell the difference between MD-80 models?
When I was at the airport a month ago I spotted a McDonnell MD-80 and took a picture of it and was very interested in this historic aircraft. I looked up the specs and this is what turned up. The MD-81,82,83, and 88 models all have the same fuselage length(147ft 8in) except for the 87 model(130ft 4in). They all have the same wingspan at 107ft 8in and the 81,82,83,88 carry 172 on a one class cabin except for the 87 which carries 139 on a one class cabin. So is there any way to tell the difference between the 81,82,83, and 88 models? The picture I took of the MD-80?

Couldn't find any good tags for this one could you maybe change them to something that sound better than plane-Identifying. Thanks.

Did you get a picture of the aircraft registration number? If so, you can just look it up.

As @GregHewgill said, if you have the N-Number you can look up the aircraft info here, on the FAA registry.

This thread has info that can at least partially answer the question.

Given that the MD-80 series was manufactured until 1999 and there are around 400 still in airline service, I wouldn't say it's particularly "historic".

If you have the date / time, you may look at Delta flights at the airport, it will give you additional information, and likely the type.

For Delta, it's either an MD-88, or an MD-82 reconfigured as an MD-88. The differences between the 81/82/83/88 are engine, fuel, and flight deck options. MD-87 is visually shorter than the others.


text:
How does an inexperienced pilot handle G-Forces?
After reading this question and the linked article, I had some more questions about G-Forces on pilots.
The article says:

The average, fit aviator has about a 3g "naked" limit, which comes
  from automatic tightening of blood vessels forcing blood to the brain.

I'm a private pilot, with no training with G-forces.  I'm average fitness (maybe even a little below average).
For the big 40th Birthday, I went to the Sky Combat Ace experience, doing simulated dog-fights in Extra 330LCs.
The instructors said that both my brother and I pulled in excess of 7G. (with no G-suits or anything beyond some grunting).
I'm not so sure I believe that now.  Were they blowing smoke to give us a fun experience?
Or could I have credibly pulled 7G for 10-20 seconds without prior experience?

Their site makes similar claims, and says that a regular healthy person will lose consciousness at around 5-6 Gs (which they can do in the Extra).

It depends on which axis you receive the Gs

On a similar topic, how does negative G forces affect our bodies?

Incorrectly performing a G straining maneuver, AGSM, will actually decrease your G tolerance.  Forcing blood to your head actually over pressurizes your brain and causes your veins to open up and dump the blood.  Your brain is much more sensitive to extra blood pressure, vice less blood pressure.  Think positive vice negative G's.  The dump valve, so to speak, is a safety mechanism.

7G for 10-20 seconds sounds unlikely to me! Human can resist way more then that but only for a very short amount of time (car crashing into a thick wall goes up to more then 30G...) but only for a very very short time. As soon as you have a longer time the Gs affect your blood flow. This will lead to unconsciousness. Fun fact: Astronauts have to resist about 3G during launch and/or landing. (Thanks to @SHAF for correction)

@Antzi There's only one axis that applies to aircraft g-loading as it relates to the human physiological response.

The  G-limit for the Extra 300 (the parent airplane to the 330):

The Extra 300 is stressed for ±10 G with one person on board and ±8 G with two

So it is certainly possible from an airplane perspective that you pulled that many Gs - in an aerobatic airplane, it's not unheard of to pull 1G less than the aircraft limit (usually there is a large margin of safety built into that number before a catastrophic structural failure).
Now did you pull 7Gs? As others have noted, 7Gs for 10-20 seconds seems very unlikely. But it is not out of the question your peak instantaneous G load was 7.
From a human factor standpoint, G-suits typically don't increase the max G-load, but rather increase the sustained G-load and the time period it can be held for. G-suits do very little to actually decrease blood flow (pooling in the legs) - they primarily serve as a reminder to the pilot to perform an AGSM.

A g-suit does not so much increase the g-threshold, but makes it possible to sustain high g longer without excessive physical fatigue. The resting g-tolerance of a typical person is anywhere from 3-5 g depending on the person. A g-suit will typically add 1 g of tolerance to that limit.

Now there are a vast array of factors affecting this resting G-tolerance. I flew  a military high-performance trainer, and my resting G-tolerance was around 3, or the lower end of the spectrum. One of the other pilots I knew had a resting G-tolerance of about 7.5. The primary difference is blood pressure. I am 5'10" and only 145 pounds, with a resting blood pressure of about 90/60-100/70. He was 6'0" and about 215 pounds, with a much higher blood pressure. Tall, skinny, nonsmoking runners have actually the worst resting G-tolerance while short, stocky, sedentary or heavily muscled smokers have much higher tolerance. Other factors, such as how hydrated and rested you are and how much stress you are feeling, can vary vastly your daily G-tolerance.
All of those numbers I just listed do not take into account the pilot performing an AGSM (Anti-G Straining Maneuver). This can add several Gs to the pilot's tolerance, and is one of the biggest things taught in physiological training for high-G maneuvers.
So TL; DR: could you have pulled 7Gs without prior exposure? It is possible, depending on varying personal factors and body type, but it is not likely. However, with a little training, 7Gs is perfectly attainable.

Its been my experience that a gsuit will increase your max resting G by at least 1-2 G's--which is significant if your resting G is 3.5, you perform a G warmup, you don't squeeze and your hose comes undone.  There have been several times I've had to squeeze the black out when I've noticed a faulty hose and was expecting my suit to inflate.  I can easily reach 5 G's without squeezing when my suit is inflating.

Why the downvote?

A normal acrobatic ride experiences 3-4 G's for a few seconds. Competition acrobatic pilots will pull up to 5 Gs for 2-3 seconds, which is risky. It is difficult to do more than this in a piston-powered aircraft. 5 Gs for more than 5 seconds will present a significant risk of a blackout or loss of consciousness in an inexperienced person. From a textbook on aeronautical medicine:

Its entirely possible that what felt like 10-20 seconds was actually only a few seconds.  It certainly felt longer. :)  But somewhere I have a video of the ride.  I'll have to re-watch that with a stopwatch. (It still won't tell me how many G, but it should give me a solid idea of duration)

Look closely.  The cockpit will be fitted with a G meter.  You might be able to see it in the video?  Oh, and 7g for even a few seconds is blackout for all but the most fit and well trained.

In the 2-seat planes used for tourist flights, the instructor/rear-seat had the full panel.  My front-seat hardly had anything (I remember airspeed... maybe attitude indicator... not much more).  Certainly not a g-meter, or I would've been watching it myself.

5Gs for more than 5 seconds is blackout. This is not at all true the way you said it, though perhaps you meant some qualifiers in there you didn't type. And competition pilots pull instantaneous G-forces in excess of 9 and several-second G-forces easily in excess of 5. Most of this is done without G-suits

The top number represents the average resting G rate (just prior to light loss) of 1,000 people.  Its not uncommon for shorter people to have resting G rates much higher.  I personally know a woman whose resting G is higher than 5.  However, even a moderate amount of squeezing can make 5 G's completely tolerable for an extended amount of time.  Furthermore, more important than the max G's sustained is the G onset rate.  An extremely high onset rate to 5G's can easily black a person out, even if they are wearing a G suit.  Also, a push-pull (negative to positive G's) is GLOC inducing.

@RhinoDriver That some people can survive high g-loads is irrelevant here. The fact is once you reach sustained 5g you are risking a blackout.  What do you think the tour operator did? Sustained 7g loads because there was only a 30% chance of them blacking out and everybody dying? Gee, only half of my passengers go unconscious during the ride so I guess that is Ok!

Certainly the operator is well versed in his own G Limits.  Anyone that constantly flies in that regime of flight is more than capable of sustaining 5 Gs.  Furthermore, that article you cited with 4.8 is resting GLOC, with no squeezing.  Id be surprised if the operator didn't know to squeeze his legs.  If the passenger GLOCs, who cares?  Aside from doing the funky chicken when he wakes up, and having some wicked awesome dreams, it's a non event and he's got a cool story.  If he doesn't LOC, then he's still got a cool story.  Sounds like a win win to me.  We put people to sleep all the time.


text:
Is it legal to use an online logbook?
I am a computer programmer and student pilot. I want to make a computer program I can use to store my logs. Can I legally do this? Can I legally store Logbook endorsements with this? Are there any rules I need to be aware of? For the signatures can I use a pilot's certificate number instead?

There are probably dozens of off-the-shelf programs at this point that do what you are asking about; those that store signatures either record them via camera or via a touch screen.

Short answer: an electronic logbook is legal; the FAA will accept almost anything as an endorsement; it's often most practical to collect endorsements on paper but electronic versions are also fine.
First, the fundamental point about logbook formats is that the FAA defines what you have to log (14 CFR 61.51), but not how you log it. And clearly electronic logbooks are "legal" in the sense that there's no law against using them.
However, I suspect that the main question you're asking is, how can I gather endorsements in an electronic logbook? AC 61-65E is essentially the FAA's practical guide to 14 CFR 61, and Appendix 1 lists recommended sample endorsements, with this comment:

The following examples are recommended sample endorsements for use by
authorized instructors when endorsing logbooks for airmen applying for
a knowledge or practical test, or when certifying accomplishment of
requirements for pilot operating privileges. Each endorsement must be
legible and include the instructor's signature, date of signature,
certificated flight instructor (CFI) or certificated ground instructor
(CGI) certificate number, and certificate expiration date, if
applicable.

So it's clear that you need a "signature" from your instructor and for most people that means paper. But you might start questioning what a "signature" really is and if you can substitute something else. Fortunately the FAA has an entire AC (AC 120-78) on electronic signatures that applies to part 61 and it says:

An electronic signature may be in the following forms.

A digital signature
A digitized image of a paper signature
A typed notation
An electronic code
Any other unique form of individual    identification that can be used as a means of authenticating a    record, record entry, or
document

That's a very broad definition of an electronic signature, although it seems clear that the FAA wants it to be "individual" and non-repudiation is a requirement:

An electronic signature should prevent a signatory from denying that
he or she affixed a signature to a specific record, record entry, or
document

However, there's also the practical question of how you collect endorsements. If you demand that your CFI creates an account in your logbook software, or generates his own digital certificate, or whatever else will make your electronic life easy, he may simply refuse. And how do get his endorsement when you're at that grass strip in the middle of nowhere with no cell signal or WiFi? How do you explain AC 120-78 to a skeptical DPE or FBO owner who's never heard of it before?
In the end, the simplest solution is often to just to get a physical signature on a piece of paper with all the necessary information as per AC 61-65E. If you then want to go digital and shred the paper, you can always scan it and add it to your electronic logbook as per AC 120-78.
But, if you want an electronic endorsement or signature and your CFI is willing to provide it, that's also fine. I use MyFlightbook for logging (no other connection and I'm not endorsing it) and their FAQ addresses whether electronic signatures are valid (links not preserved from the original):

The FAA does accept digital signatures, and outlines the criteria for
doing so in FAA circular AC No: 120-78A. While we believe MyFlightbook
is compliant with this AC (and we explain why we believe MyFlightbook
is compliant here), the FAA has thus far not indicated willingness to
even evaluate, much less certify, online logbook systems for
compliance.

My personal experience so far has been that DPEs have no problem with accepting electronic logbook printouts and endorsements. If something seemed suspicious then I assume they would investigate and ask some questions.

There is seriously an advisory circular for everything.

The requirements for a signature seem a bit contradictory; how does "a typed notation" "prevent a signatory from denying that he or she affixed a signature to a specific record, record entry, or document"?

I've been using myflightbook.com for a couple of years now.  It is free, easy to use, and very comprehensive.  I've flown over 100 different aircraft types and am rated in several different categories so it's important to me that the elogbook that I use is capable of handling all of the oddball piloting stuff that I do and myflightbook does it all.
As to the question about endorsements.  The FAA does allow for electronic signatures as one of the previous posters correctly pointed out (AC 120-78) and myflightbook supports this feature which is a good way to collect endorsements for "dual received" flights.  With respect to endorsements that give a pilot an operating privilege, such as high-performance or a flight review, you can have the instructor write it out on paper and then snap a pic of it with your smartphone.  Then just attach or upload the pic to your elogbook.
The last time I needed an R44 SFAR flight review the instructor asked for my logbook and I just slid him a piece of scratch paper and snapped the pic.  Myflighbook allowed me to quickly type in the flight entry and attach the pic.  I've also had to show a part 121 carrier that I was going to work for my logbook and they were fine with a printout from my elogbook.
I hope that helps answer the question.
Regards,
  Alan Brown
  ATP: ASEL, AMEL, LR-Jet, SA-2000
  Commercial: Helicopter, Glider, ASES
  CFI: ASE, AME, IA, Glider


text:
Has there ever been a plane not controlled from the nose?
Has there ever been an airplane where the pilot, or cockpit were not located near the nose of the airplane?

Not a plane, and not really not the nose, but in the Mi-24 helicopter ("Hind") the gunner sits in the nose with the pilot's cabin above/behind. (However, both can shoot and fly if need be.)

Do RC aircrafts count?

NASA added a second cockpit to their Boeing 737-100, located in the forward cabin.
History is a bit patchy, but I believe this was initially to see if it was possible to fly the plane by camera. This might be required by a supersonic design where windows would be impossible (also known as a 'virtual cockpit'). I understand it has been used for all sort of experiments since then.

NASA 515 is the first B-737 built. First used by Boeing to qualify the 737 for airline service, the prototype 737 has since been heavily modified by NASA. It has two separate cockpits - a conventional B-737 forward cockpit providing operational support and safety backup, and an operational research flight deck positioned behind in what was the aircraft's first-class cabin section.

The full list of projects involving this aircraft are listed on their website.

Credits: NASA

Credits: Museum of Flight

Was there a specific reason why the second cockpit seems to directly use an original plane cockpit, other than the simple reuse of control panel components for the prototype? In particular, did things actually look like depicted in the schematic? The idea that a second cockpit would literally look like the chopped off front section of a second plane mounted into the outer plane otherwise looks like it comes from a bad scifi movie that runs low on set design budget.

@O.R.Mapper, NASA probably did have a low set-design budget.

@Vectornaut: My comment was mostly aiming at the question whether they really painted the inner cockpit the same way as the plane on the outside ;)

The second cockpit was actually more for testing avionics and navigation equipment, especially for IFR flight, so forward visibility wasn't really needed. There is an interesting report about the test plane that goes into more detail.

@O.R.Mapper is it possible they dropped in part of a simulator?  Alternatively that was artistic licence: "How can we draw a 2nd cockpit"?

@O.R.Mapper  The may 1979 issue of Popular Science shows a picture of the 2nd cockpit from the rear.  It appears to be a freestanding installation like in the graphic; but no other details can be discerned from the camera angle.  https://books.google.com/books?id=iwEAAAAAMBAJ&pg=PA84&lpg=PA84&dq=NASA+++737+two+cockpits&source=bl&ots=04JrLhwdkI&sig=Y7bjK3bipM_08WxZ4v9yx52tRoQ&hl=en&sa=X&ved=0CFAQ6AEwC2oVChMIhKHLw8C9yAIVgc6ACh0VxAhx#v=onepage&q=NASA%20%20%20737%20two%20cockpits&f=false

@O.R.Mapper - the idea was to test whether a plane could be flown by camera. The easiest way to do test this is by using a cockpit which is familiar to the pilots: otherwise if there's a problem you have an extra factor (pilots unfamiliar with the interface/layout etc) in your results: you have no idea if the issue was from the camera, or whether the pilot just couldn't find the controls. It's simplest to simply duplicate the environment the pilots understand. As to colour scheme.. that was probably just the easiest way for the person making the picture to create it :)

The Museum of Flight has a virtual tour of this aircraft here: https://my.matterport.com/show/?m=qnHM6q5zmPU

Some of the Gee Bee racing planes are obvious candidates. In fact, in one of them the pilot was right next to the tail:
Gee Bee Model R

Image Credit: Wikimedia Commons
It needs no guessing that the Gee Bee planes were explicitly attempts at shoving the most powerful engine into the smallest and lightest possible air-frame, with the pilot tucked in somewhere. This philosophy, their handling characteristics, and several serious injuries and deadly accidents meant that the models acquired a reputation for being death traps.

Similar: Me 209.

Jimmy Doolittle disagreed. In the Wikipedia article on the Gee Bee model R Doolittle is quoted (from the Springfield Union of September 6, 1932) as having said, "She is the sweetest ship I've ever flown. She is perfect in every respect...". This was, however, an airplane with a big honkin' engine on the front, small wings, and small control surfaces which did not tolerate inattention on the part of the pilot. Stall or add throttle too fast (or both, in sequence) and they'd smear you across the landscape. Not a beginner's airplane, but flyable.

Most of the (single engined) piston aircraft had the cockpit after the engine, This resulted in the cockpit being aft of the wing, like the Supermarine Spitfire.

"Ray Flying Legends 2005-1" by Original uploader was Bryan Fury75 at fr.wikipedia - Transferred from fr.wikipedia; transferred to Commons by User:Padawane using CommonsHelper.. Licensed under CC BY-SA 3.0 via Commons.
The F4U Corsair's cockpit was set so far aft that it caused visibility problems for pilots landing in carriers.

There are somewhat frequent accidents with WWII era plans running over much smaller planes because of this problem.. you can't see stuff on the ground in front of you, and WWII era planes are considerably larger than many smaller recreational aircraft.

Is that really a military aircraft with a big target and "Bozo" written on it? That sounds like a very, very bad idea and a self-fulfilling prophecy.

Many civil and military aircraft between 1920 and 1950 had their pilot in the center of the aircraft, or further aft. Random selection:

1922: De Havilland DH37 (source).
Not really aft, but interesting offset from the longitudinal axis:

1938: Blohm and Voss BV 141 (source).

1939: SAI Ambrosini SS.4 (source).

1942: F4U-1 (source).

1944: Spitfire Mk 19 (source).

Just collect all tandem-seater trainers where the pilot sits in the aft seat so the trainee will not change the center of gravity. They all need to be flown from the back seat.

Wow, that 1938 Blohm and Voss BV 141 has to be about the ugliest plane I've ever seen

@Kevin: You'll like them too: Caproni Stipa | V-173 | Y.1S | XG-85 | M-57 | X-24A, ...

Did the BV1 help inspire the Millennium Falcon?

@Polyergic No, the design of the Falcon was changed at the last minute from something that looked too much like the Eagle from Space 1999. The shape is said to be inspired by a half-eaten hamburger next to an olive on a stick. The Falcon's cockpit is definitely inspired by the B-29.

@mins, the Caproni Stipa looks like it was the inspiration for Bullet Bill from Super Mario Bros.

The original design for the Falcon got slightly bulked up and became the corvette that Leia's traveling on at the start of A New Hope.

Would I be correct in guessing that the reason the passenger seat was usually placed closest to the center of mass, with the pilot behind, was to allow a plane to have similar handling whether the passenger seat was occupied or vacant?

@supercat: Absolutely correct! A tandem configuration sometimes has a limitation for solo flight to be conducted exclusively from the rear seat. A well know case is the famous Piper Cub that has been the training aircraft for many pilots. The trainee seat is likely over the CG, and cannot unbalance significantly the aircraft.

The 1906 plane of Santos-Dumont was controlled from the rear side.

The plane of Santos Dumont

Adding to the excellent existing answers, flipping through my copy of The World's Worst Aircraft (because we've learned putting the pilot anywhere but the nose is a terrible idea), I find some... umm... interesting and unique pilot arrangements.
The B.E.9 placed the pilot behind a large protruding pod where the gunner sat in front of the propeller. As you can imagine, gunners were not thrilled with this arrangement.

The "Boeing" (actually a US Army design, Boeing just built it) GA-2 had the pilot in an armored housing in the middle of and on top of the airframe.

The Loening PW-2 was a "high"-wing monoplane with the pilot sitting under a wing mounted so low they had no forward visibility. And this was a pursuit fighter! That's ok, the pilot could see fine when the poorly attached wing tore itself off.

Please attribute your photos

@CGCampbell All are in the public domain by now. They're attributed to their collections in the image descriptions, except the first which I don't have a source for. Would you like something different?

It's not technically an airplane, but I thought I might mention the BV-347, which was an experimental variant of the CH-47 Chinook that Boeing built in the late 60's. Changes included a longer fuselage, retractable wheels, and a pair of rotatable wings.

However, one of its weirdest features was a gondola that could be lowered which faced the rear of the helicopter. It had a set of controls and the helicopter could be flown from there. The gondola is the mesh structure below the nose.

So not only could the BV-347 be flown from a position that wasn't the nose, it wasn't even facing forward!

Good find! Interesting - the 2nd picture doesn't appear to have the swing wing of the first

Please attribute your photos

@FreeMan, It looks to me like the wing is in the second picture, but we're looking at it edge-on, so it's almost invisible. The rear is just above the second black circle from the left (I assume a window), and you can see the shadow of the wing as a black stripe just under the wing itself.

@MichaelS My understanding is that they did actually remove the wing in the latter stages of testing. From what I remember (I'm on my phone at the moment but I will try and find the source later) they determined that while the wings led to a significant increase in performance, they also led to a substantial increase in pilot workload. I believe Boeing then removed the wing to assesses the performance of the other modifications, such as the longer rotor blades, and lengthened fuselage. I'll see if I can find where I read that when I'm next at my computer.

I guess I'm just seeing the stubs where they removed them. This page has some more detailed images and it does seem the wings would droop down and be more obvious even from the edge.

Interesting: at the bottom of the page which you linked it says that the wings could be detached and stored within the helicopter when not in use. Perhaps I am misremembering what I read and instead of removing the wings, they just detached them and ceased wing testing.

Cheating a bit:
X-24B (a lifting body test craft that helped validate the concept for the space shuttle):

(Credit: NASA)
Cheating quite a bit more:
The F-82 Twin Mustang:

(Credit: USAF, Jack Dean.)
White Knight II:

(Credit: D. Miller. http://www.flickr.com/photos/fun_flying/3820887625/.)

Since you didn't specify the type of aircraft, here is one type not controlled by nose :)
This is what we do all weekend (Although that is not me)

Image source:  https://cdn.gardenidea.us/medium/4/jet%20rc%20airplanes.jpg

In a similar vein to the BV-347 example the Erikson Air Crane company operates a Sikorsky S-64 Air Crane with a rear facing cockpit that allows a pilot to fly the aircraft with a less restricted view than they would have from the cockpit - especially helpful when trying to precisely place an item it is carrying/delivering.
Black arrows denotes where the cockpit is.

The main flight cockpit still faces forwards though.

As does the main cockpit of the BV-347 and NASA 515. Key is that all 3 could be flown from the auxiliary/secondary cockpit.

Neither the Lilienthal glider nor the Wright Flyer were "nose-controlled".
(Depending on how you define "aircraft".)
In the early days, the weight of the pilot pretty much defined the center of gravity, which had to be near the center of the aircraft.

Lilienthal glider, picture in the Public Domain.

Wright Flyer picture CC BY-SA 4.0 by D Ramey Logan.
Others have given answers with lots of examples and pictures. I wanted to point out the historic angle:
Aircraft didn't become "nose-controlled" until rather recently. In the beginning, the pilot was nearer to the center than the nose.

In the Boeing 747 the pilots sit quite far behind the lower deck of (usually) first class seats downstairs. Quite noticeable in row 1 when the plane passes through hail.

authors: Bob Jarvis - Слава Україні


text:
How can I calculate a flightpath given a set of waypoints?
I have made a GUI that allows the user to create waypoints defined by latitude, longitude, altitude, and time-of-arrival. I'm looking for some software that can generate a flightpath between the waypoints.
For example, say that I have placed 5 waypoints. All that I know is that I want my aircraft to be at those five points in space at the times specified. To create my 'flightpath', I want to calculate the latitude, longitude, altitude, pitch, roll, yaw, and velocity of the aircraft as it moves from one waypoint to the next. I'd like to calculate those values for time intervals of, say, one second.
I've made a hackish solution, but it isn't very realistic. Someone must have tackled this problem before. Does anyone have any suggestions on software or algorithms I can use?

What do you mean by "simulates a flightpath"? Do you mean drawing lines between them, or animating the progression through them over time?

I hope I addressed what is needed. I do not mean drawing straight lines between then, I mean a progression through them over time.

It's more related to maths than to aviation. An actual flightpath has other constraints (performance, weather / wind, ATC rules...) that are not part of this geometry problem.

It is a very math heavy problem; however, I thought that aviation folks would be more likely to know if such software exists. If my question is not appropriate for the aviation overflow, then I understand, and my apologies.

I want to calculate the latitude, longitude, altitude that's a flight planner, I agree but pitch, roll, yaw, and velocity that's more a flight simulator to me.

Nice question, I 've done this in the past. How realistic does it need to be? What are your requirement on accuracy. what is the purpose of the program. What kind of aircraft are you trying to do this for, do you have access to an aircraft performance model for the aircraft? Do you take wind into account, and other meteorological aspects?

The main thing is I just want the velocity, pitch, and roll profiles to be smooth. So if you plot these values versus time I'm wanting the plot to be smooth as in the mathematical meaning of the word.
I'd like to leave the aircraft model as simple as possible. I have an aircraft class in my GUI with some values like maximum pitch, maximum roll, maximum acceleration, maximum speed, maximum altitude, etc.

If all you're looking for is calculations of ETE, ETA, headings, fuel burn, and other such items you can make use of the FAA's DUATS platform. Skyvector has some basic capability in this area as well.
You'll have to chase down the actual aircraft performance data to input into the software if you want realistic estimates, but the internet is awash with information manuals and operating handbooks for the more widespread families of light aircraft. Google is your friend for this one. As for numbers between waypoints, the simple and lazy, but often sufficient, solution is to simply interpolate.
Commercial solutions exist as well such as ForeFlight and AOPA's FlyQ, but I doubt they would add anything of substantial value for your particular needs.

Thanks those are some great leads! I think this is the closest answer that I'm gonna get. Thank you so much.

@StephenHartzell - something occured to me. Are you trying to implement a program where the user inputs a series of waypoints and times that they want to be over those waypoints at and the program returns the parameters that they must fly at in order meet those times? In this case, there would be several ways that you can go about this. If you wanted to build everything from scratch, you could look into linear programming (maybe nonlinear too) techniques. Gradient techniques might also be helpful if you can efficiently piggyback off existing flightpath calculation solutions.

Also, if that's the case, this question might be more appropriate for the math, DataScience, or SO SEs, depending on your focus.

You are correct, but I was also searching for any known software that does that. That's why I thought it was appropriate for this the aviation stackexchange. My current approach is very mathy, and like i said it works ok'ish. I was just searching to see if there was already a solution (which probably does use advanced mathematical techniques).

@StephenHartzell - a perfectly reasonable assumption to make. I suggested the other SEs if you were looking for specialized knowledge to help develop the solution. With respect to figuring out airspeed and flightpath, I would imagine that proprietary software does exist, or at least the capability might be embedded in dispatch software packages, as both the airlines and the military need to engage in a certain amount of flight profile optimization to make schedules work, and it would be time consuming to figure it all out by hand. Not sure how that would be helpful to you, unfortunately

The Haversine equations will calculate the bearing and distance between any latitude/longitude pair, and can calculate the location and next bearing for points along a Great Circle.
They go back to the days of sail, shortly after the invention of the marine chronometer, which allowed calculation of the current longitude. As such they assume that the points are on the surface of an idea sphere; as Earth is slightly oblate, there is an error of upto 0.6% in calculations of locations. For any realistic altitude, the oblateness (23 km difference between polar and equatorial radius) is likely to be larger than the change in altitude.
A discussion of them is here http://www.movable-type.co.uk/scripts/latlong.html


text:
What radio frequencies are used for intercom in formation flying?
What radio frequencies are used for air-to-air intercom in formation flying? I assume there is a difference between military and civil aviation (e.g a group of GA aircrafts flying as a formation).
I found a couple of civil UNICOM frequencies here (e.g. 122.8 MHz, 122.975 MHz, ...). 122.750 MHz (Aviation Air to Air Communications) seems to be what I am looking for (correct?). But what if there is more than one team?
I also wonder if in military or professional formations (aerobatic formations) something outside the Very High Frequency (VHF) Aviation Band is used (to provide better quality, e.g. digital communication).
In this article I can see lot of military frequencies, but not telling me what to use for military formation flying.

For the US, according to section 4-1-11 of the AIM (Designated UNICOM/MULTICOM Frequencies) for private fixed-wing flights you should use 122.75:

Air-to-air communication (private fixed wing aircraft): 122.750
Air-to-air communications (general aviation helicopters): 123.025
Aviation instruction, Glider, Hot Air Balloon (not to be used for
  advisory service): 123.300, 123.500

I have no idea what the military does and their tactical comms might even be encrypted anyway, but they frequently use UHF instead of VHF, at least in the US.
Nor do I know what to do if you have two formation flights at the same time, but I guess that in reality it's either an air show with some form of semi-official control and perhaps even NOTAMs, or it's something private and in that case people make their own arrangements, e.g. picking some frequency that doesn't overlap with any nearby assigned frequencies. Using 123.45 is apparently common, but definitely not official.
Non-VHF communications for private flights would be regulated by the FCC, not the FAA, and personally I'm not sure if the benefits would be worth the extra equipment and the risk of confusion, but then again I know nothing about formation flying.
There's some useful information from the FAA in this policy order clarifying the use of 121.5 and 123.45. It says that 123.45 is for operational use in oceanic regions, and within the US it's reserved for "non-government flight test operations". There's also an FAA document on requesting temporary frequencies for airshows etc. but it's air to ground only.

123.45 is called "numbers." sometimes a friend will hear you pop up on a frequency and say your name or tail number and "numbers," e.g. "bob -- numbers" or "5 4 fox-trot, numbers." That means they want you to come up on 123.45 on your other radio.

For general aviation, 122.75 is the official fixed wing air-to-air frequency designated by the FCC and FAA (and 123.025 is for helicopters). There are also other frequencies allowed based on location (Hawaii, Los Angeles, and the Grand Canyon). Otherwise, you should probably ask around in the area in which you plan to operate. See if there is a frequency that is commonly used. This thread mentions a few frequencies people have used. If you can find the frequencies used for a local air show, that could be a good indication of frequencies that would be free.
Military aviation is going to vary a lot more. Typically UHF is used, but certainly VHF or digital could be used depending on the situation. Refueling tracks have designated areas and frequencies. Performing groups have a set of channels that they use when they fly. For regular formation flying though, it will probably vary more.
RadioReference is a good place to look. 123.45 is listed as "unofficial" air to air and flight test. The military table lists 303.0 as a possibility.

What does the FCC say regarding just picking a frequency? For example, if I went flying and knew a buddy was also in the area, could I text him "go to 133.875" and that's totally legal, assuming it's not used in the area?

The US Military uses UHF frequencies.  Each organization has a communication frequency for contact if you need to divert, have an emergency, or need guidance from higher authority.  When in formation, they have a tactical (often called 'tac') frequency to talk to the other plane(s). However most communication of a non-tactical nature is done on traffic control frequencies.
ATC handles formations as a single flight.  Each member of the flight has a number Lead(1), 2, 3, etc.  The Lead does all communications with ATC.  If you are directed to, for example, change altitude, the lead plane acknowledges with call sign and 'climbing to FL240'   The number two aircraft just responds "Two" and the number three responds with "Three" and so on.  If you do not have a tac frequency and you need to have a conversation with another plane, you tell them to go to an informal channel like Winchester or Popcorn.  Winchester is 303.0 MHz.  These informal channels were used extensively in Viet Nam to discuss what idiots the brass were.  Pilots had a code sheet that had a code for common expressions.

do you have some sources? also, would you mind cleaning up the language a bit and formatting your answer for better readability?

With respect to military aviation, it's going to depend on the radio capabilities of the aircraft involved in the formation. fooot's answer mentions that typically UHF is used. That is sort of true - UHF is generally used for military ATC, RAPCON, etc, but as far as aircraft-to-aircraft, it will depend on the capabilities of the plane.
Many large aircraft have multiple radios, UHF and VHF, as well as digital radios, so depending on the mission, they may use a specified area frequency, or a "local" frequency, or a specific military channel. With smaller aircraft, such as trainers and fighters, they may only have 1 of each (UHF/VHF), so with the need to monitor the controlling agency, that may drive the "formation frequency" to using a VHF.
With regards to specific channels in that article, it will vary from location to location, as different bases/squadrons/aircrafts will have different frequencies designated for formations. So there's no real way to know "in general" - it would be a localism.

Could one specify what Navy F18s are using? Or is this still too unspecific?

@HorstWalter - I'm USAF, not USN/MC, so I don't know. And unfortunately I don't have any contacts that fly that, so I can't be more specific


text:
Is there a Take-off speed category?
ICAO Annex 14 recommends that "Runway centre line lights shall be provided on a runway intended to be used for take-off with an operating minimum of an RVR of the order of 400 m or higher when used by aeroplanes with a very high take-off speed, particularly where the width between the runway edge lights is greater than 50 m." (section 5.3.12.4).
I wish to know whether aircraft are categorized by take-off speed (like they are by approach speed), or which aircraft fall in the category of having very high take-off speed.

Never heard of any sort of takeoff speed "category" applied to operators in US rules, but we do have rules (in an airline's OpSpecs) for our aircraft that tell us at what min visibility centerline lights are required for takeoff (and landing as well).
If an airport were considering investing in Centerline Lights, that recommendation, combined with a little research into the requirements of the airlines who'd potentially operate into & out of that runway, would provide a basis to determine what incremental gain in utilization the runway could have. (Along with some meterology hisoric data -- numbers of hours/days at or below a given RVR value.)
The term very high take-off speed does seem a little nebulous; airliners' takeoff speeds are pretty high compared with most General Aviation aircraft, and unless you're building a runway for fighter or experimental jets, there aren't that many aircraft with higher takeoff speeds than we have that it would seem worthwhile to install CL just for them.
But, who knows... Maybe another ICAO document does define that term somewhere.

Modern fighters have relatively low wing loading to be able to pull tight turns and this also gives them reasonable take-off and landing speeds. Only the 3rd generation jet fighters like F-104 had really high take-off and landing speeds.

Thanks Mr. Ralph and Mr. Jan, if there is no such categories are defined, why did ICAO uses the term as a condition to provided RCL lights? As Mr. Ralph said may be some other doc may have reference about it.

Perhaps it is simply descriptive, rather than intended as a strict ("V1 at max T.O. Weight > 161 KIAS") definition.  Fast takeoffs/landings, you need them; slower speeds, not as much.


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How do helicopters turn using rotor?
I know that airplanes use rudder to turn, and use elevator for nose up and down.
How do helicopters change their altitude and how do they make turns?

Related question - http://aviation.stackexchange.com/questions/2036/what-are-forward-flight-straight-flight-level-flight-and-cruise-flight-in-a-h?rq=1

Are you asking about the physics of turning or how the controls are used to turn?

Airplanes do not use their rudder to turn; they do it by banking into the direction of the desired turn, then the wings "lift" the plane in that direction.  The rudder is only used to maintain lateral trim, so that the airflow doesn't impinge on the side of the fuselage and drag is minimized.  To initiate a turn, the pilot uses the stick or yoke to actuate the ailerons on the wingtips, causing the wing on the inside radius of the turn to go down and the wing on the outside radius of the turn to go up.  A slight back-pressure of the stick or yoke raises the nose, causing a "climb" to be initiated, but since the plane is banked toward the center of a circle, the "climb" doesn't cause a change in altitude, instead it causes the plane to fly a circular path.  Small, simultaneous changes in engine power and rudder deflection are needed in order to maintain proper trim and constant altitude in what is called a "coordinated turn".
Helicopters turn in a manner analogous to that of an airplane.  In forward flight, the cyclic stick (between the pilot's legs) is pushed slightly in the direction of the desired turn, causing the rotor disc to tilt, just as the wings of an airplane are tilted in a banked turn.  The collective lever and throttle (at the pilot's left side) are adjusted as needed to maintain altitude and the rudder pedals are adjusted to maintain a coordinated turn.  Since the fuselage of a helicopter is suspended from the rotor hub like a pendulum, as the helicopter enters the turn, the fuselage tends to be flung outward, so it banks, just like the fuselage of the airplane that is rigidly connected to its wings.  (In a hover, with no forward airspeed, a helicopter can turn in any direction with the rudder pedals alone, something an airplane cannot do.  In this special case the fuselage remains level.)
To change altitude, it is necessary to add power to climb or reduce power to descend.  This is true of any heavier-than-air aircraft, as, for a constant velocity, increasing altitude implies increasing potential energy and decreasing altitude implies reducing potential energy.  In helicopters in forward flight, a climb is accomplished by first pulling back slightly on the cyclic stick to raise the nose and establish a climb attitude, then raising the collective lever and twisting the throttle grip on the collective lever to maintain constant rotor speed.  As the collective is raised, the pitch of the main rotor blades increases, giving them more "bite" on the air and, therefore, more lift.  A skilled helicopter pilot will perform these actions in a coordinated manner, such that everything appears to happen simultaneously.  In the special case of a hover, a helicopter can climb and descend with the rotor disk in a constant horizontal attitude.  As described above, the collective lever is raised and power is increased with the throttle to put more energy into the system, raising the aircraft; to descend the collective lever is lowered and power is decreased with the throttle.  Directional control in a hover is maintained entirely with the pedals; if the helicopter is the most common type with an anti-torque tail rotor, moving the rudder pedals requires the throttle to be increased or decreased slightly to compensate for the varying power consumed by the tail rotor and to maintain constant altitude.
(If this sounds complicated to you, you're right.  Rotary wing flight is considerably more difficult than fixed wing flight, and it took decades longer to perfect helicopters after fixed wing aircraft had taken to the skies.)

There is one thing I'd love to see expanded a bit here, and yes I realize the FAA gets it wrong. That is: the rotor disk does not just tilt because you moved the stick - I would like to see an explanation of cyclic pitch and precession added here.

Indeed, the rotor does not tilt, the whole helicopter does. The cyclic simply changes lift differently on different sides of the rotor by varying blade pitch depending on their current position.

@JanHudec "the rotor does not tilt" - it most certainly does.  The rotor tilts first. followed a short while later by the fuselage which acts like a pendulum and "follows" the disc.

@JanHudec Let me give you a concrete example.  On sloping ground, the disc should be level with the horizontal before lifting.  This is achieved by tilting the disc, quite significantly sometimes, then lifting.  The disc will stay horizontal and once clear of the ground, the fuselage will swing level underneath it.  It feels very strange the first time you do a lift from a significant slope.

@Simon: Nevertheless the rotor hub does not have any tilting hinge. The cyclic does not tilt anything, it changes blade pitch differently by position. The blades flap accordingly, so the result is that the disk tilts, but it's not the rotor as a whole, it is the blades flapping individually. (So saying the rotor tilts is not really wrong, but it is misleading as to how it works)

Ah, cross purposes :)  We are both saying the same thing.  It's the distinction between the "rotor" and the "disc".

Although the blades flap through differential lift, saying the rotor doesn't tilt puts you at odds with every pilot, every CFI, and the FAA's way of talking about it. It's like saying "the engine doesn't drive the wheels on a 4wd car. The engine drives. Each wheel individually," which may be true but misses the point.

Helicopters don't have rudder pedals

@rbp But the pedals controlling the tail rotor blade pitch have the same effect as the rudder pedals in winged airplaines: the push (or pull) the tail to the left, or right, so the direction of the whole thing changes.

Then why not call the cyclical the steering wheel?

There is no steering wheel. There are two controls controlling the same thing: Collective (controlling main blade pitches in an all-at-once manner), and cyclic (controlling the main blades' pitches depending on their position on the rotor circle). Collective is one control (one handle that can be moved in one direction, ie. forward and backward), and cyclic is the second (the main "joystick", two dimensions, forward/backward and left/right). No wheel in sight.

I think rbp is aiming at the misnomer of "rudder" pedals for... what's the correct word for the pedals in a heli?

The collective is two controls. And unlike an airplane in which the stick is two one-axis controls, the cyclic is one two-axis control. There are plenty of airplanes that have steering wheels http://www.conniesurvivors.com/pictures/N494TW-27Feb99-Cockpit.jpg . the pedals in a helicopter are properly called anti-torque pedals and control yaw. they are not rudder pedals or tail-wheel pedals, and they don't necessarily control anything on the tail (http://aviation.stackexchange.com/questions/8642/how-can-a-helicopter-be-designed-without-a-tail-rotor/8643#8643)

@TheBlastOne the anti-torque pedals don't have the same effect as the rudder in an airplane, as you would find out in MCA in an airplane, or in a helicopter with LTE

Airplanes can and do use the rudder to turn.  Granted, most of the time they do not but while doing some radio testing we wanted to keep the antenna pointing towards the ground so we did flat turns up to 8 hours a day for several weeks.  Talk about a left leg workout!

@rbp, to avoid the nomenclature issue, some texts just call them "pedals".  Since the rotor systems on coaxial or tandem rotor craft inherently cancel torque, to generally call them anti-torque pedals would be incorrect.  I called them "rudder pedals" in this discussion for the purpose of illustration, likening them to the rudder of a ship, which controls yaw.  I have yet to encounter a text that calls them "yaw pedals", though.

even coaxial rotors don't completely cancel torque, and the pilot still needs to yaw the aircraft with the pedals to keep the nose pointing where she wants.

@AndrewP. Hey, i see you mentioning the pedals being used for turning or turn stabilization depending on flight mode, and then adjusting the throttle for changes in tail rotor power, but i don't see any mention of the pedals' method of action being changing the pitch/power/whatever of the tail rotor or related device.

@StarWeaver — If I understand your question correctly, on a helicopter with main rotor and anti-torque tail rotor, varying pitch of the tail rotor blades with the pedals to get more or less 'bite" on the air and yaw the craft requires more or less engine power, respectively. To keep constant altitude in hovering turns requires making coordinated throttle adjustments by twisting the grip on the collective lever, depending on direction of the turn. The pedals have no mechanical link to the throttle. The effect is less evident when main rotor is in translational lift, as when in forward flight.

A helicopter has 3 separate flight regimes: normal flight, autorotation, and hovering.
In normal flight and in an autorotation, a helicopter pilot initiates a turn by applying left or right pressure on the cyclic, the control stick between the pilots legs. Through a series of control rods or actuators, the cyclic causes the swash plate to change the pitch of the blades of the rotor, depending on the position of the blade in its cycle.
To turn the heli, more lift is needed on the outside of the turn than on the inside. Taking into consideration gyroscopic precession, the swashplate adjusts the blades so that the blade pitch is highest on the outside of the turn and lowest on the inside of the turn, which causes the rotor disc as a system to tilt to initiate the turn. In a semi-rigid rotor system, the entire disc actually tilts on the teetering hinge

In a fully-articulating rotor system (via the flapping hinge) or on a rigid rotor system (flexible blades), only the individual blades move, although they all move in concert to generate the effect of the entire disk tilting.

Once the disk starts to tilt horizontally in the direction of the cyclic, the fuselage will follow it along, and the heli rolls into the turn. Once the desired bank angle is established, the cyclic can be neutralized, and the increased airflow over the rotary wing on the outside of the turn will maintain the aircraft in the turn.
Since all the controls on a helicopter are strongly-coupled, the pilot will need to adjust the pitch, yaw, and power in order to control the heli's altitude, fuselage heading, and airspeed, and to correct for ambient conditions such as wind and turbulence.
In hovering flight, the helicopter pilot turns the helicopter by use of the anti-torque pedals, which control the yaw axis of the aircraft. And indeed, one can "turn" a helicopter during a flight without initiating it with horizontal movement of the cyclic. To do this,  slow the aircraft to a hover, yaw the aircraft to the desired heading, and re-initiate forward motion. Don't try this in your airplane!

Good one. Peace, man! (But where is the tail rotor -- no mention?) (Hope you won't hate me for that?)

see "yaw" in second-to-last paragraph

There are three controls in a helicopter:

Cyclic stick (this cyclically changes the pitch of the blades, creating different amounts of lift at different points of the cycle)
Collective lever (this determines the force generated by the rotor)
The anti-torque pedals (they control the tail-rotor)

This picture shows the result of moving the cyclic. As you can see, the whole rotor is turned, causing the helicopter to move in a certain direction, as shown in this image by AVstop

The collective determines the amount force generated by the main rotor
The anti-torque rotor is used to rotate the helicopter, as shown here, obtained from Gunschip Academy:

The main rotor will induce a torque on the cabin, making it spin. A force is needed to prevent this spinning. The tail-rotor provides this force, keeping the helicopter-cabin straight.
However, if we want the cabin to rotate, we can adjust the blade pitch of the tail-rotor. This will change the force delivered by the tail-rotor. The imbalance in moments will then rotate the cabin.
It should be noted here, that all the movements are strongly coupled. Any input will always have additional side-effects, which need to be counteracted.

“Cyclic stick (this changes the disk plane of the main rotors).” No, it does not. It changes blade pitch differently depending on their position.

You're right, I'll change my answer.

That change made your answer the best one.

The only thing I am missing in the answer is a statement about the fact that usually, the tail rotor is spinning at constant speed, and the force created by it is controlled by that blade pitch change. Also, the aspect that to keep the heading constant, the tail rotor must generate a "base" force to counteract the torque that is generated by spinning the main rotor. (That´s why a heli without tail rotor might fly, but it would rotate on the main rotor axis, in the direction opposite of the main rotor spin direction.) The picture hints into that direction, but the text does not comment on it.

Not every helicopter has a tail rotor. The pedals control yaw, regardless of the mechanism. I would also urge you to disassociate collective from up/down. It adds/removes energy from the system, which could be altitude or speed (see "strongly coupled"), which is also true for forward / reverse cyclic.

The only helicopter that is a "real" helicopter (capable of hovering) and has no tail rotor is one with two main rotor blade discs installed on the same axis, but spinning in opposite directions, or with more than one main rotor, with their axes installed in different locations (Chinook). OK, or one that has an alternative "force generator" where a jet engine exhaust generates just the same force a tail rotor would generate (NOTAR systems).

here are 6 "real" helicopters that use non-tailrotor designs http://aviation.stackexchange.com/questions/8642/how-can-a-helicopter-be-designed-without-a-tail-rotor

All of which fit into the categories I´ve outlined...

As I read it, I think this question was about the 'standard'-helicopter, thus featuring a tail-rotor. In order to keep the explanation simple and concise, I therefore only explained this type of helicopters.

Think of a triangle of vectors.
When the rotor disk is exactly level, the thrust from the rotor acts vertically.  If you tilt the rotor, you now have a slightly reduced vertical thrust (the thrust vector) and a horizontal component which will apply a force to the helicopter in the direction of that horizontal component.
As ROIMaison states, the cyclic control tilts the rotor disc as required.
Please excuse my lousy drawing skills.

Disc level

Disk titled

Because the vertical component is now reduced (the total thrust is the sum of the vertical and horizontal component), the helicopter will descend slightly since the vertical thrust no longer balances the weight.  Therefore, a small increase in power is required achieved by increasing collective pitch.  The engine then creates more torque which must be balanced with opposite torque from the tail rotor, achieved by moving the opposite pedal forwards.
As in all aircraft changes, there is a primary effect (tilting the disc in the direction of travel) and secondary affects of increased power and increased torque.  This is why flying a helicopter needs adjustment of all three controls together.
To climb, you adopt a climbing attitude, by pulling back on the cyclic, which causes the nose to rise.  Because the horizontal component of the total rotor thrust is now reduced (since the disc is now titled forward less), your speed will reduce unless you increase power by increasing the collective pitch which increase the horizontal component.  This will need an input on the pedals to balance the correct torque.
To descend, you reduce power, which reduces the total rotor thrust.  Since the vertical component no longer opposes the weight, the helicopter will descend.  Since power is reduced, the horizontal component of the thrust is reduced and the helicopter will slow down.  You push forward on the cyclic to increase the horizontal thrust and maintain speed.  Of course, a pedal input is required to counter the reduced torque from the engine.

The disc does not tilt by itself. There is no mechanism on board to tilt it. Instead, rotor pitch is varied along the rotational axis so the blades generate more (or less) force on the left (or the right) disc sector, and AS A RESULT the disc tilts. I.e. the helicopter climbing and the helicopter turning ("tilting") rely on only one mechanism: blade pitch variation.

In fact, since the rotor is rotating, the pitch change is done 90° away from the place where the desired "tilt" is wanted, just like to make a turning wheel "tilt" left, you have to apply a force 90° away from the rotational axis (i.e. to turn left, you turn the wheel right in a plane 90% away from the axsis). (Sorry for my humble English.)

ROIMaison states "Cyclic stick (this cyclically changes the pitch blade, creating different amounts of lift at different points of the cycle)", which is something different than "tilting the disc". There is no specific hardware for the tilt. Collective and cyclic both control the blade pitch. Collective does it equally for all blade "location" on all circle sectors, while cyclic changes the blade pitch differently for different circle locations.

the teetering hinge tilts the entire rotor

@TheBlastOne I am aware of all this, being a helicopter pilot, but for this particular question, for the OP who clearly is not, thinking about the triangle of vectors whose size and shape is controlled by tilting the disc and/or changing power is a useful explanation. Otherwise, I could write 1500 words to include the differences in attitude and altitude control in different phases of flight to include dyssemmetry of lift, inflow roll, blowback, translational lift, tail rotor couples etc etc. Of course, moving the cyclic results in tilting the disc but is this really relevant in this case?

Well, I'd say yes, but your perspective might be a different one. For me, personally, it was a real "aha!" when I learned that the tilt is a result from the same piece of hardware as the upward thrust, namely: rotor blades, with pitch variation. Until then, I kept searching for the "tilter" on helicopters, and nobody understood what I was asking for. So I am not saying that I know better. I am just trying to point out that this is an aspect that is imho central to understanding where the "tilt" comes from.

Turn Control
In order to effect a turn a lateral acceleration (horizontally to the left or right relative to the direction of the vehicles motion) is needed. Consider a bicycle leaning towards the center of a turn.
In an aircraft primarily two things happen.

The ailerons are used to bank the aircraft towards the center of the turn in order to tilt the lift vector.
Particularly in slow aircraft the rudder is used to adapt the rotation of the aircraft around the vertical axis to the changing direction. This ensures that no sideslip occurs, i.e. that the aircraft always points exactly in the direction of flight (in reference to the air).

Once a helicopter has significant forward speed the same principles apply. Via the stick the cyclic rotor control is used to bank the helicopter (slightly) towards the turn center. The torque pedals are then used to coordinate the turn (sync the change in direction with the turn speed of the helicopter).
Altitude Control
In order to change the altitude the flight path needs to be increased or decreased. Also two things need to happen.

The flight path needs to be changed via a short vertical acceleration (to bend it).
Then the aircraft needs to be stabilized / trimmed to maintain this path.

For fixed wing aircraft there are actually different techniques to do this.
The most intuitive is to change the pitch of the aircraft via the elevator. Upon descending or climbing the thrust (engine setting) needs to be adapted. (A glider will adapt its speed accordingly).
Another technique with classical fixed wing aircraft is to reduce (sink) or increase (climb) the engine power / thrust level.
Helicopters make use of their direct control of the lift via the collective control. (Subsequently this results in a change of rotor torque which needs to be compensated via the pedals and the engine settings.)

I guess you are not a helicopter pilot. This is too simple an explanation for helicopters. To climb, you first adopt a climbing attitude by pulling back on the cyclic. This starts the climb. Since the total thrust vector is now more vertical (you are climbing) an increase in power is needed to maintain speed (a helicopter can climb or descend with zero forward or backward speed). As more power is required, trim changes are required to maintain direction. You do not start a climb by pulling collective since this will result in an increase in speed. Descending is power, then attitude, then trim.

Helicopter in forward flight behaves just like airplane in all manoeuvres and uses the same sequence of control inputs. Only hover is special.

But helis don´t have ailerons, at least they don´t require them.

@Jan Hudec maybe the point is that most helicopters turn their main rotor disc AT CONSTANT SPEED at all times. More power means steeper blade pitch, not larger rotational speed.

@TheBlastOne: Helicopter don't have ailerons, but they have lateral axis of cyclic that has exactly the same effect on the aircraft and even quite similar principle. And it's totally irrelevant; I said same control inputs, not same control surface movements.

@TheBlastOne: Modern helicopters have constant speed rotors; the early ones required pilot to adjust throttle together with collective (one control element—up/down for collective, twist for power) to maintain the speed in acceptable range (and even with constant speed rotor the pilot has to pay attention to rpm, because he could loose rotor speed by exceeding maximum available power)

@JanHudec "Helicopter in forward flight behaves just like airplane in all manoeuvres" this is completely untrue. when you say "constant speed rotor" you're thinking like an airplane pilot, and the phrase makes no sense to a heli pilot

@rbp Yeah. But current state of art is: blade pitch control. I wouldn´t answer the question with yesterday´s state of art. It does not contribute to understanding how today´s helicopters work. In contrast, it confuses more than it clarifies. Also, there is a good reason why rotational speed now is usually constant, and blade pitch the primary control: It just works faster, is more secure (though more complicated to implement), and thus better in general. And nobody said rpm is not important.

@JanHudec Not true.  Are you a helicopter pilot?  I've got a few hundred on helis and a couple of lessons in fixed wing.  Control inputs are very different and, not in the same order.  There are some well known killers in helicopters which catch fixed wing pilots transitioning, for example, countering negative G.  They do not behave just like a fixed wing, nor are inputs in the same sequence. For example, what happens in a fixed wing if you reduce power, and leave all other controls where they are?  Now try this in a helicopter (actually, don't, you may well die).

@JanHudec  Here is an even simpler example.  Please tell me which fixed wing control provides the same functions as the collective lever?  Since you assert that the control inputs are the same, there must be one?

@Simon: Stick corresponds to cyclic, power to collective. I now realize there is a difference though; aircraft is longitudinally stable, so it will respond to increase in power by pitching up and vice versa which a helicopter, being unstable, won't.

@JanHudec  The collective does not change power.  It changes the pitch of all blades together.  On some helicopters, not all, there may be a correlator or engine management computer which will demand more or less power if pitch is changed but that is not the primary function of the collective.  Power is controlled by the throttle or a FADEC or similar computer on jets.

@Simon: The collective does not change engine power, but it changes rotor power, that is the rate at which the rotor adds energy to the kinetic+potential energy of the craft, so for manoeuvring it behaves just like power in fixed-wing aircraft. To climb an aircraft you add power, to climb a helicopter you add collective (and pitch up in both). The fact the energy initially comes from rotational energy of the rotor that is subsequently replenished by correlating the engine power is the part specific to helicopters, but modern ones usually have automatic correlator so pilot does not care.

@JanHudec You are confusing power with thrust. Rotor thrust varies with collective but power does not since without increasing work done by the engine (energy over time), the total energy in the system is the same, IAW conservation of energy.  Without a power change, you cannot gain potential energy without losing kinetic energy and vice-versa.  If you were to increase collective pitch with no change in power, you would rapidly stall the blades since you are converting kinetic energy to potential energy (and increasing drag significantly).  I am not aware of any definition of "rotor power".

@JanHudec  The power required by the rotor is dependent on total rotor thrust but power is only derived from the engine, unless you convert one form or energy to another.  This is exactly what an autorotation is.  You are trading potential energy for kinetic energy.  According to you, a helicopter could still climb if the engine failed!  Finally, to climb a helicopter in forward flight, you use cyclic, not collective.  I think it might help to state what experience you have since there is a lot of confusion here.

@Simon: When the engine fails and the pilot pulls the collective up (instead of pushing it down as needed for auto-rotation), the helicopter will briefly climb. It will however quickly slow down the rotor and then it will obviously crash.

@JanHudec Hi Jan.  I'm going to give up.  You were wrong to say that helicopters behave like fixed wings and have the same control inputs in all manouveurs except for hover.  The is just plain wrong.  You are also wrong about "rotor power" but since you have not stated your qualifications, nor have you read up on the appropriate references, I see no point in going on.  Cheers

I so far experienced,the co-axial helicopter turns in forward flight or in hovering 360 degree turn,both can be done by reducing pitch angle of the opposite rotor(Clock wise or Anti-clockwise rotor) of turning direction which will be acting as torque effect as like a single rotor helicopter without tail rotor.

Can someone clarify the relationship between aircraft speed, torque, prop length and pitch and how this applies to a helicopter.

Mentioned all terms are inter-related Speed- depends upon the torque(Engine Power)-Length of the blade/prop-the -lifting capacity of the helicopter depends upon on the blade area/disc loading-subsequently-Torque-pitch-to increase lift and thrust also depends on the engine power(Torque)-and all these are applied by the cyclic, collective and correlator governor and co-ordinated by mixer control unit. to make some one understand,it might take a long lecture which might take several hours.

In addition I want to know if the amount of lift a helicopter generates changes dependant on pitch, how much does the pitch change?

To determine the actual changes of pitch angle for a certain amount of lift is a mathematical calculation,if you are to find out this in definite figure,you are to know the helicopter aerodynamics with mathematical terms.In a nut shell,you can say,the more lift is required,the more should be the pitch angle and the more should be the engine power.
Thanks